This competing renewal examines how blood pressure regulation differs between blacks and whites. There is increasing evidence suggesting that blood pressure decreases (or "dips") less at nighttime in certain groups of individuals and that such relative non-dipping of blood pressure is related to adverse health outcomes. Data suggest that non-dipping is found more frequently in Blacks. We will study 80 blacks and 80 whites in an effort to understand the psychological and physiological correlates of nocturnal BP dipping. Patients' sleep and ambulatory blood pressure will be studied at home and in the Clinical Research Center environment. Physiological characterization will include 24-hour urinary norepinephrine, beta-adrenergic receptors on lymphocytes, hemodynamic responses to behavioral stressors, heart rate and blood pressure responses to infused isoproterenol. Psychological characterization will include assessment of life stressors and job stress, mood, anger/hostility, and social desirability.